This invention generally relates to an apparatus and method for spray coating articles or parts, and particularly to a spray coating apparatus which provides an enclosed atmosphere for a continuous spray coating process.
In general, it is known to spray paint articles by means of an apparatus having a conveyor system which introduces parts to an open spraying booth where a plurality of spray nozzles will coat the surfaces of the article with a paint composition. A variety of paint compositions may be used, including paints which are dispersed in various solvents or dilutents. The use of solvents may present the possible risk of explosion or health risks from overspray from the open spray booth. Alternatively, a water-based paint may be used with overspray problems presenting less of a risk, but resulting in inefficient paint utilization when such overspray is exhausted to the atmosphere. Open chamber spray-coating apparatus, with the associated overspray problems, provide a relatively wasteful coating apparatus and process.
Attempts have been made to contain the overspray in closed chamber apparatus, having inlet and outlet openings. Attempts have been made to limit the escape of coating material through the inlet or outlet such as by air or water curtains. In such a system, coating material within the air of the spray booth can be circulated and possibly reclaimed. Such attempts have required a curtain of fluid at a discharge outlet of an air circulation system or make up unit associated with the spray booth, or the use of an air curtain at the open entrance and exit to the spray booth. Although the provision of an air curtain at the entrance and exit openings of the chamber does increase efficiency, the high-volume air flow of such systems still results in loss or escape of coating material and may not eliminate safety or environmental risks. The circulation of air within the spray chamber also results in an undesirable atmosphere within the chamber which allows curing of the coating composition within the chamber.
Efforts have also been made to recycle excess coating material which has not been applied to a part. Efforts to recycle coating material include providing the supply of coating material in a reservoir formed in the bottom of a coating chamber, with excess material falling into the reservoir. Alternatively, an open return drain is coupled to an external supply of coating material. In each of these cases, the recycled coating material is exposed to conditions which allow it to begin curing, possibly preventing it from being reused in the system or resulting in clogging of spray nozzles or other systems of the apparatus.
Other disadvantages of known coating processes and apparatus include the inability to readily modify the position of spray nozzles within a coating chamber to a desired position relative to a part to be coated. Depending upon the configuration of a part to be spray coated, it would be desirable to allow selective repositioning of spray nozzles within the coating chamber for optimizing the coating process relative to any particular article being coated. Further, spray nozzles used in prior art apparatus are susceptible to being clogged by the coating material, requiring the nozzles to be cleaned which generally results in halting operation of the machine for affecting such cleaning procedures. Regular cleaning of the apparatus is also required, resulting in significant undesirable dowtime in a continuous coating operation.